Standing wave coupler



Oct. 22, 1946. H, M, STRQBEL 2,409,991

` STANDING WAVE COUPLER Filed April 12, 1941 Coupling `Jealicm of Line,

Fi g. 41 IN VEN TOR.

Patented Oct. 22, 1946 UNITED STATES PATENT OFFICE sTANDiNc WAVE poorten Howard M. Strobel, Allegany, N. Y. Application April 12, 1941, serial No'. 388,279'

4 Claims.

This invention relates to a high frequency generating system of the type which is energized by successive groups of charged particles moving through space, wherein thegroups are obtained by delecting a stream of charged particles.

The object of the invention is to provide improved method and means for generating highfrequency `currents of highl power and for controlling-the deection mode of `a high velocity stream of charged particles. Y 1

-In conventional methods of utilizing high velocity streams of charged particles for high-irequency generation, the stream is either inter. rupted into groups, or deected from side to side by energizing a xed pair ofi'deflector plates. VIn the latter casel collection ofthe deected stream is effected in such a manner as t charge rst one side and then the other of some oscillating circuit. There are certain limitations imposed when using the `conventional stream deflection methods. For one thing, the high velocity charged particles can only be actedV upon by the deflecting held during the interval of time it takes each of them to pass the xed deflecting plates, and the higher the velocity the shorter'is this time interval. Increasing the length of the delector plates will increase the time `interval it takes a charged particle to pass through the eld between them, thus giving algreater amplitude of deflection, but also increases the minimum-oscillation kperiod that may be applied tothe deilector plates, sothat increased amplitudes of deflection of the stream are obtained at the: expense` of a decrease in frequency. Because of the above and other difficulties, the known conventional methods of utilizing high velocity streams of charged particles Afor high powered high-frequency generation are limited in their practical application.

This invention relates to an improvedmethod for generating high-ireduenciesl at high power which consists essentially in directinglong a given path a stream of high velocity charged particles and .providing along the path aseries of changing delecting fields whose polarity is so coordinated with the velocity of the charged particles that a given segmentV of the streamnof charged particles is'actedupon byaeld of substantially the same polarity throughout the length of the given path.` For creating ,the desired type of dellec'ting field, it is proposed that a transmission line which isadjusted and erlergized so as to set up electromagnetic'standing waves be used. As is wellknown .toV the art, travcling waves can besetup in any of the conventional transmission linels, such as, for example,

the open wire type or the coaxialtype. A standing wav'e is the resultant of an incident traveling Wave'and its're'lected traveling wave traveli ing in opposite directions over the same transmission path. The conditions for .terminating the line so that reflected waves will result is well known to the art, and'consists in general of a mismatch termination. `When a transmission line is thus energized with astanding wave, at`

half wave length section of the line in a time interval of one-half a period of the exciting frequency, then it follows that some given charged particle will always be acted upon by a eld of the same polarity throughout thelength of the path. That is, if a charged particle is justentering a one-half wave length section as its trans-` verse deflecting, field is turning positive, the field of the following section will just be turning negative in polarity; by the time the charged particle traversesthe first section, it will just be turning to negative polarity while thefollowing section will just be turning positive as the particle `enters it. The maximum amplitude of deflection of the waved stream will occur when the moving charged particle can` traverse a-Wave length, section of the given path inA atime period of theifrei quency coordinated with the given wave length; The amount of dellection that any one` 'charged particle will receive for each wave length section depends upon its instant of1 phase entry into the field coupling section; if it enters at the instant of zero eld or phase, it will receive maximum positive deflection; if it enters at the one-quarter or three-quarters instant, due to subsequent cancelling fields itwill receive zero deflection; and if Vit enters at the one-half phase instant, it will receive maximumpnegativedeflection. As a result, the emerging stream of charged particles will have a waved shape, and the positively and negatively deflected j loops ofthe waved stream can be `used to energize an oscillating circuit.

`When the velocity of the charged'particles,is

such that they traverse one wave lengthI section in the period of one cycle, the maximum amplitude of deflection of the resulting waved stream is obtained. However, the velocity of the charged particles may be greater or less than the above assumed optimum value. vFor a given phase instant of entry into the coupling section, it is possible to make the displacement amplitude of the waved stream on emerging to be either zero, or some positive or negative value, depending upon what fraction of the optimum velocity is selected.

In this method of creating aseries of varying fields lalong a'given path a transmission line, which by denition is made up of distributed electrical'constants or parameters, is used to create a'Vv l standing wave eld. It would be possible to ap,- proach this result by using properly phased lumped constants for each one-half waveA length section of the given path forming the coupling` section. For practical application, the use of the transmission line has greater advantages.

It will be noted that the wave coupled oscillatoror amplifier using a standing wave on a resonant transmission 4line can be excited from either end of the line, whereas the wave coupled oscillator or amplifier using traveling waves as disclosed in application having Serial Number` 388,280 and iledAprilA 12, 1941 must be so excited-that the traveling wave and the electron stream are both movingfin the same direction. Y

The method of using the fields of a standing Wave to4 derect moving charged particles gives many advantages over known systems. Brief reference to some of these advantages may be made. It will be notedthat for a given strength of field finthe standing wave, the amplitude of deflectionof the stream for a given velocity can be ,made'as large as desired simply by increasing the length of the coupling section of the transmissionl line. Also, the amount of power that can be controlled is not. limited by the usual cons-iderations of physical size of the apparatus. Further, very high frequencies can be generated or amplified without encountering the many.y difcul-V ties inherent in other systems wherein the physicalv size of the apparatus imposes severe limita'- tions'. Other advantages 0f the invention will be wave pattern are vshown as of the coaxial typ. Figure l is a block diagram showing the main elements of the stationary wave coupler. Block Ill represents a gun for creating high velocity charged particles, such as electrons. In what follows, it will be assumed that the charged particles used are electrons, although it will be obvious that this is not a necessary restriction. Block II represents the coupling section, wherein the fields of the standing wave and the electrons of the electron streamare coupled together, sothat the wave elds deflect or displace the electrons therein.

Block I2 represents a high-frequency collector for ,y collecting high-frequency energy from the waved stream of emerging electrons. Block I3 represents the loadwhich utilizes the energy collected by the high-frequency collector I2. Block I4 shows the high-frequency nergizer which energizes the transmission line of the coupling section II, and thus forms the stationary wave pattern therein. `"Ihe high-frequency energizer I4 may be anindependent oscillator, or may be energized by a portion of the output energy of the high-frequency collector I2, Y Y

In the operation of the wave coupler, the electron gun I directs a stream of electrons along the ,path in the coupling section IIV where the standing wave field pattern is set up. A transmission line can be used to direct the` path of the Wave. Conventional transmission lines consist of such members or media as will tendj to guide electromagnetic waves 'along a given path. One conventional type of transmission line consists of t-wo spaced 4parallel wires. In order that standing waves shall be formed when the transmission line is energized, it is necessary that traveling waves moving in opposite directions be set up in the transmission line and coupling section. If one end of the line is energized from a high-frequency Vsource and the other end terminated in such a manner as to create a reevident. from the more detailed description that Y A follows.

' -Morel particularly, the invention consistsin the system and method.` hereinafter'described, illustrated inthe accompanying drawing and dened in4 the-claims hereto appended, it being understood that `various changes in form, arrangement and details both of circuits and of method within the scope ofthe claims lmay be resorted to without departing from the spirit or sacriiicing any of the advantages of the invention. I

Aclearer understanding of the operation of the invention and its 'improvement overknown methods canbe obtained by reference to the following figures and the descriptions relating thereto.

i :Figure 1 showsa block diagramfof the principal elements ofthe standingwave Vcoupler used as an oscillator or as an amplifier.

Figure 2 shows'arcircuit diagram of a high-freflected wave, the desired standing wave eld'will result. 'As iscommonly known Vin the art, such reflected waves will be set up if the end ofthe line ismismatched as by being open-circuited or shortf-circuited. The standing wave will form a series of one-half wave length sections along the coupling section II whose fields are alternately of positive and negative polarity, and wherein i the field cfeach section varies sinusoidally with time at the frequency ofthe energizing source III- v By directing electrons of given velocity through the standing wave transverse electro; Staticelds of the coupling section the action of the fields yon the passing electrons of the stream ser-Vegte` deflect the stream into a waved pattern. 'i StillV referringv 'to Figure l, if the highfrequencyenergizer I4 is an independent oscillator energizing the coupling section I I; all of the output energy of the collector I2 goes to theload I3.'V Under these conditionsthe standing wave coupler serves as an amplifier. However, by diverting part of the output of collector I2 to the coupling section vII, the vstanding waveV coupler serves as an oscillator, "In the matter of-the fre-` quency at which the oscillator willoperate, itis to be rememberedthat a'transmission line setting up standing waves is in the nature of `a resonant line, and thatthe resulting resonant frequency is a function of :the length of the resonant line, in which Vthe fundamental or harmonic frequencies may be used. Y A

Figure 2I shows vav circuit diagram of the standing wave coupler used as anamplierjfor aandeel high-frequency currents.' The exciting oscillator 26 energizes the transmission line 22-.23 oi the coupling section, which includes two spaced parallel conducting members 22 and `23. The electron `gun 2l directs a stream 0i high velocity electronsthrough the `coupling section 22-23 as is indicated by the dotted lines. The .end of the coupling transmission lineA ZZ-i is terminated with animpedance 26 Ywhich'may have an infinite or zero value in order to favor the forming of standing waves in the coupling section. Highfrequency energy is collected from the waved electron` stream by s.the collector plates 2l' and 2S and the high-frequency collector circuitZ trans- -fers the energy to the load 2e. A ground return circuit from the collector 2li to the electron gun circuit 2l `is provided. The tube casing 29 per- -mits evacuation of the air frorn the region through which the electron stream is directed.- The standing wave formed in the coupling section of line ,22--23 `is represented graphically .by the voltage curve shown at 3.9. The condenser plates 3 l-32 and 33--34 indicate where one-half wave length sectional elds could be set up if a series of. such condensers were energized in proper phase.

By reference to Figure 2 the operation of a wave coupler using standing wavesand operating as an ampliercan be made clear. The coupling section 22-23 of the transmission iine is energized by the oscillator 29 and the line so terminated as to create standing waves. The electrostatic eld set up between the conductors 22-23 by the stationary waves is illustrated graphically by the voltage curve in graph 3u. The transmission line is shown as marked on in one-half wave lengths to correspond with the voltage curve, and theA one-half wave length seg-4 ments are indicatedby the letters a, b, c, d, c, and the remainder by f. The ,primes of the above letters indicate the corresponding regions of the graph. The electron gun 2l directs a high velocity stream of electrons along the straight dotted lines shown. The voltage curve 3B` shows the range of values that the standing wave goes through for a complete period or cycle, It will be observed that the zero nodes are successive stationary points at one-half wave lengths along the line, whereas the loops vary with time between maximurn positive 4and negative values. Flor any given instant, say, the loop .'iil--a' will be lpositive, .3B-19' negative, SEB-c positive, and so on throughout` the coupling section used. One-half aperiod orcycle later, however,` the polarity of the respective segments will be rei versed. Ifa stream of `charged particles is directed through the standing wave field with such 'a velocity that each particle traverses a one-half wave length section in one-half a period of time, the amount of deflection that a charged particle will receive for each wave length section it traverses will `depend upon the phase of the standing wave at the instant of entering the wave length section. A particlaior example, entering Sil--a' at the instant of zero phase, will be entering just-a5 the held `a--IJ/ is turning positive, and will be leaving just as it is turning negative; consequently, it will be entering lthe next section Sil-b justas itis turning positive, and `similarlythroughout the rest of the path. As a result, a particle entering the coupling section at the instant of zero phase will receive a -maxi- 'mumldeflection'in the Lpositive direction. By a simiIa-r'line Aof reasoning, a particle entering the Ycoipling-'section -SU-a/ at the instant` of- 1809 phase, will receive va maximum `deflection in zthe negative direction. It follows that particlesentering at the instants of and 270 phase `will receive zero deflection `for .each complete wave length traversed, since the elds in say, SU-a and .til-b' will change `polarity while the particles are traversing them, and thus substantially cancel out `any deflections. Particles entering` the coupling section at phase instants between `.those mentioned will receive intermediate amounts of deflection, so that the nalemerging stream of charged particles or electrons will .leave vthe coupling section waved into a sinusoidal Wave iorm. Aiterobeingwavedin the coupling section, the` electron stream impinges uponthe` collector plates 2l and 28. It will be observed that those electrons that were for `the most part in thepositive polarity eld Aand were thus displacedupwards will bei collected on the upper plate 121;, While those that were for the most part in the negativepolarity eld will be collected on the lower plate 28. The result will be to alternately charge the upper and lower plates` with eleotrons, and so energize them ata frequency which islproportionate to the number-ofpulses collected per second. A

It is-to be observed that the standing wave pattern in the coupling section 2.2-23 'as illustrated by the standing wave. graph 3E? couldbe duplicateclby `the use of individual lumped impedance oscillating circuits Vspaced in series along `the pathof the electron stream. `lior` example, the eld inthe section Sil-11' could "be duplicated b3" a pair `of condenser platesI 3'l-32` energized by an oscillating circuit. Likewise, the eld 'in section `lill-c' could be set up between the'conden'ser plates 33 34 by energizing them from an oscillating circuithaving the proper phase relationship. It follows that a properly spaced and energized series of such pairs of condensers vwould set up a series ofelds approximating the standing wave eld pattern setup by the coupling section of the transmission line `{l2- 2%. In comparing the two methods, it is evident that the wave propagationmproperties resulting from the distributed electrical constants inherent in the transmission line construction provides a simpler means of producing the desired held pattern.

Figure 3 shows a diagram of a wave coupler using standing waves when used as an oscillator. The electron gun is represented by the cathode element 46 and the plate lil, eachI connected in the conventional manner to energizing sources.

The coupling `section is formed bythe spaced conductor elements d2 and 43; The electron stream is collected by the collector ,plates 4t and' 45,' and thereby energizes the collection` circuit 46. 'Bhe circuit 45 may be tuned to some-desired frequency, and energy isfed `therefrom to Vthe load 4l and the coupling sectionM- `The connections between the coupling section-42-43 and the collector circuit 6 must be ofthe proper phase necessary to maintain oscillation of the wave coupler. The head lend of the eouplingisection line 42443 is shown open-circuited, thereby reflecting waves and creating a standingwav'e eld along the coupling section; `A ground return is provided from the circuit 46 to cathode di? for electrons of the stream'. The tube casing lepermits the air to be evacuated from the rregion through which the electron stream is directed.

u The operationof the wave coupled-oscillator using'standing waves is fundamentally:theV sante as that of `the amplier in Figure 23' "It diners 7 mainly in ithat it uses its own developedhighfrequencyenergy to energize the coupling section. `Also, thecoupling section 42-43 is energized from the collector end At6, instead of from theelectron gun head end. It is to be noted that awave coupled oscillator using a traveling wave onlymust be so energized that the electromagneticwave and the stream of charged particles are both moving in substantially the same direction, Vwhereas in the Wave coupled oscillator using a standing Wave this restriction does not apply. With regard to the frequency at which thewave coupled oscillator operates, this can be stabilized by a `proper choice of L. C. constants in the highfrequency collector circuit 4111-45-46, which frequency may be the fundamental or a harmonic of the resonant line coupling section 42-43. In the diagram the electron stream from the gun l0-4| is shown as three straight dotted lines in its unexcited position, whereas the single waved dotted line indicates the waved-electron stream after excitation.

Figure 4 shows a wave coupled oscillator utilizing Vstanding Waves, but in which the coupling section transmission line is depicted as of the coaxial type. The electron gun 5U directs a circular ring of electron streams into the coaxial coupling section of the transmission lineV which has an outer cylindrical conductor member 5| and an inner conductor member 52. The collector ring plates 53 and 54 collect the high-frequency energy and thereby energize the toroid oscillating circuit 55. The load 56 is coupled to the fields set up in the toroid by the loop 51, The coaxial line coupling section 5I-52 is energized from the toroid 55 end of the line. The end of the line is shown as open-circuited, which will give the reflection o-f traveling Waves necessary for setting up standing waves in the coupling section. For the -purpose of permitting evacuation of any air in the region through which the electron stream is directed, an air tight surface can be formed by the outer coaxial member 5I, the toroid 55, and the casing 58 surrounding the electron gun 50. The paths that the streams of electrons follow in their normal and in their waved form are shown by the dotted lines.

The operation of the wave coupled oscillator of Figure 4 is fundamentally similar to that of Figure 3, the main difference being that the fields used are guidedby a coaxial line. Highfrequency energy is collected from the waved electron stream by the .ring plate collectors53 and 54. In the matter of choice vof operating frequency, the toroid 55 and theline 5I-52 can be designed to operate at some particular frequency,.or'means employed for varying the L. C. constants of the toroid 55 and also ofthe length of the resonant coaxial line 5l-52. As an illustration, the head end of the coaxial line 5l-52 could be short-circuited by a movablelpiston to permit varying the length of the resonant line, proper provision being made, of course, for the entrance ofthe electron stream. o y

vThe above description serves to illustrate the general principles of the wavecoupler when using standing waves, and particularly as applied to amplifiers and oscillators.v In vthe illustrated coaxial type of coupling section,`it was assumed that a radial pattern of electrostatic field was being generated alongthe coaxial line. Other patterns are known to the art, and Vcould be used in lieu of the radial pattern, as long astlie electro,- static fields V.thereof canact to deflect the electron stream and suitable collection means are employed.

The displacement amplitude of the waved electron stream. that emerges from the coupling sec. tion will be some function of the velocity of the electrons. The amplitude of displacement will be a maximum when the electron velocity is such that an electron can traverse a Wave length section Of the line during the time interval Yof a period or cycle of .the exciting frequency. Changes of electron velocity from this optimum value will result in a decrease in amplitude, due to the fact that successive fields acting upon a given electron during its passage throughthe coupling section may not all be of the samepolarity. The displacement amplitude for given conditions of electron velocity, standing wave pattern, and coupling section length can be derived by mathematical means well knownto the art. Y f

It is to be observed that the velocityof propagation of the traveling waves along the transmission line depends upon the value of the distributed constants of the transmission line.

is lowered, then for a given exciting frequency the corresponding space length of the wave-length along the line is likewise reduced, as is also vthe electron velocity required to give the maximum displacement amplitude of the waved electron stream.

In coupling sections referred to in the drawing, the dielectric medium separating the conductor members is assumed to be space. However, as long as a path is provided for the electron stream, regions of the separating dielectric can be of material substances, such as of glass. For a given spacing of conductors, the introduc-V tion of a glass dielectric would increase the capacity per unit length of the coupling section, and so modify the velocity of the propagated traveling waves, incident and reflected. It follows that the glass dielectric used could also serve for the casing of the tube, so that in effect the conductors for the coupling section could be placed 'outside the tube walls. In some applications of the wave coupler, this form of construction might have physical or technical advantages.

With regard to the particular form that the coupling section may assume, it is to be noted that considerable variation is possible as long as the basic requirements of an electromagnetic standing wave having an electrostatic field com- Y ponent capable of deiecting an electron stream are fulfilled. If thel two wire transmission line and the electron stream, such asis illustrated in Figure 2, are takenas a basic element, it can be used to trace out other forms, as by displacing it laterally along aline perpendicular to theplane of the'basic element pattern, or by revolving. it laterally around a given line serving as an axis to create a surface of revolution. In the former case, the coupling section would have the form of two spaced, parallel conducting sheets, with a moving sheet or stream of electrons directed between. In the latter case, if the axis were parallel to the transmission line element and the radius was-constant, the coupling section would be similar to the concentric circular cylinders of a coaxial transmissionline, substantially as illustratedin Figure 4. Y

, iLgIn1 ajhigh-frequency'generating system inclillingal sectionV of a coaxial transmissioniline and bien Yelity ,Qharged particles.Y said @axial If the propagation velocity of the transmission line transmission line being adapted to set up an electromagnetic standing ywave having an electrostatic eld component transverse to the annular space within said coaxial line when energized. by a high-frequency source, means for terminating one end of said transmission line with a resonanting chamber, means for energizing said transmission line with high-frequency energy, means for maintaining a low pressure region within said coaxial transmission line, means-for directing a stream of said high velocity charged particles into said coaxial transmission line and in the eld of said standing wave, whereby charged particles of the stream are deflected by fields of the standing wave, and means for collecting highfrequency energy from the deflected stream oi charged particles. a

2. In a highfrequency generating system 1ncluding a section of a coaxial transmission line and a source of high velocity charged particles in a low pressure region, said coaxial transmission line being adapted to guide an electromagnetic wave along a given path, said section of said coaxial transmission line being open circuited at one end and terminated at the other end with a substantially toroidal shell having an annular slot therein, the outer edge of said slot being conductively joined to the outer conductor of said coaxial line, and the inner edge to the inner conductor of said coaxial line, two substantially concentric annular collector rings adapted to fit coaxially within said coaxial line, the outer annular collector ring being conductively joined to the inner conductor of the coaxial line, and the inner annular collector ring being conductively joined to the outer conducto-r of the coaxial line, means for directing said high velocity charged particles along said path toward said collector rings, means for maintaining a low pressure region along said path, and means for coupling a high-frequency load to said terminating toroidal shell.

3. In a high-frequency generating system including a section of a coaxial transmission line and a source of high velocity charged particles in a low pressure region, said coaxial transmission line being adapted to guide an electromagnetic wave along a given path, said section of said coaxial transmission line being open circuited at one end and terminated at the other end with a resonant chamber which joins the inner and outer conductors of said coaxialline, two substantially concentric annular collector rings adapted to t within said coaxial line and having transposed connections to the inner and outer conductors of said coaxial line, means for directing said high Velocity charged particies between the coaxial conductors and toward said collector rings, means for maintaining a low pressure region along said path, and means for coupling the generated high frequency energy to a load device.

4. In a high-frequency generating system including a section of a coaxial transmission line and a source of high Velocity charged particles in a low pressure region, said coaxial transmission line being adapted to guide an electromagnetic wave along a given path, said section of said coaxial transmission line being open circuited at one end and terminated at the other end with a conductive toroidal shell having a substantially annular slot therein, the outer edge olf said slot being conductively joined to the outer conductor cf said coaxial line, and the inner edge to the inner conductor of said coaxial line, two substantially concentric annular collector rings adapted to rlt coaxially within said coaxial line and having the outer annular collector ring conductively joined to the inner conductor of the coaxial line, and the inner annular collector ring conductively joined to the outer conductor of the coaxial line, means for directing said high Velocity charged particles into said coaxial line and toward said collector rings, means for maintaining a low pressure region along said path, and means for coupling a high-frequency load to said terminating toroidal shell.

HOWARD M. STROBEL. 

